For new barrel extraction rates, the recommended ratio is 2 - 2.5 oz. of Oak Cubes for use in a 5 gallon carboy. We always recommend that you start with the lighter ratio (2 oz.) for first time use, as you can always add more oak after 8 weeks.
We recommend a minimum contact time of 8 weeks to allow for the full integration of the oak flavors. Also, as you will be aging the wine on the Oak Cubes for a year or so, you may want to bring the ratio down even a little lighter.